Method and system for television communications



. May-21, 1940. T. T. GOLDSMITH. JR

METHOD AND SYSTEM FOR TELEVISION COMMUNICATIONS 3 Sheets-Sheet 1 o a n3. S o 252 3.5 5.30 5.2 2.2 E.

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twist! INVENTOR worms 1- sows-m1 T. T. GOLDSMITH. JR I 2,201,309

METHOD AND SYSTEM FOR TELEVISION COMMUNICATIONS May 21,1 '0.

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signos' to fiiiien l8. iliu Mont Laboratories, c., Passaic, hi. it,a-corporation oi ilieiawnre (on. it's-tbs),

My invention relates to hnprovements in meth-= ods and systems fortelevision counication.

This application is a division of my application Serial No. 3.955%, diedMarch 12, was.

in the more sucoessiui methods and systems proposed heretofore iorteievision communication, and employing a cathode-ray pick-up tube atthe transformer and a cathode-ray viewing tube at the receiver, it hasbeen required that there be ateach station two circuits for deflecting'the scanning rayat the line and field frequencies, respectively.disc, it has been required that line and field pulses be transmitted onthe samecarrier wave as the video signals, and these ps have been usedat the receiver for synchronization. ln thme prior methods and systs,not only has"= cu1ty been encountered in holding the deflecting circuitsat the receiver.

iocked in step with those at the transmitter, but a substantial portionof the transmitted energy hasbeen expended in transmitting the synchro-.o-Iif 1|; P111888, I I ith the foregoing in mind, it is one of theobjects of my invention to provide an improved methodand system fortelevision communication employing cathode-ray tubes at both sta-.tions, and in which no synchronizing pulses are required to betransmitted to the receiver, and in which eitherthe deflection circuitat the line frequency or both deflection circuits at the line and iieldfrequencies, respectively, can be omitted at the receiver. j

Another object of my invention resides in the provision of an improvedmethod and system for television communication which has advantages overthose proposed heretofore in the way of greater simplicity ofconstruction and manner of operation, and higher efflciency.

Another object of my invention resides in the provision of animprovedmethod and system for television communication by which thevarious necessary signals can be transmitted by wireless oversubstantially greater. distances than it has been possible with thevarious methods and systeins proposed heretofora-tho possible range ofwireless transmission from the transmitting station directly to arecelvingstation being of the order of hundreds of miles.

Other objects and advantages will hereinafter appear.

1 In accordance with my invention, voltage waves at the respective. lineand field frequencies are generated at the transmitter andtransmitted byradioto the receiver. These same waves are applied to cause or at leastgovern scanning ac- 1 must of necessity be always in step during thescanning action. Because of the impossibility o of this system gettingout of synchronization as to both line and frame or field frequencies, amuch higher interlace ratio is possible. This allows a given detailpicture to be transmitted over a much narrower frequency band. Likewise,the transmission of much higher definition pictures over the samefrcouencyband can also be accomplished.

Another advantage, of this system is that it will receive pictures oftransmitters operating at 1 any desired line and frame frequencies. Withthe present systems, it is necessary that all transmittersoperate withexactly the same respective scanning frequencies if all receivers are tobe capable of receiving fromazpny one of the trans- 2o mitters.

My invention resides in the improved method and system of the characterhereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof isshown in the drawings,

wherein 1 Figures 1 and 2 are simplified, diagrammatic views of atelevision transmitting station and a television receiving station,respectively, con- 30,

structed and operating in accordance with my invention;

Figs. 3 and 4 are graphical representations of electrical wave formspossible for-use in my improved system for governing the scanningaction; and

i Figs. 5, 6 and 7 show circuit details for use in my improved system.

In Fig. 1, the reference numeral l0 designates acathode-ray pick-up tubeof a conventional 40 construction, and comprising a' mosaic,photoelectric screen on which a light image of the object is projected,an electron gun for-generating a ray of electrons directed at thescreen, and two setsof deflecting plates for deflecting the electron rayat the line and field frequencies respectively so that it is caused toscan the screen. The picture or video signals are thereby developed, andfed by an output connection H to a. modulating amplifier l2. 1

In my improved system, but one ultra-high frequency carrier is used forall four signals, i. e.,-the horizontal and vertical sweep signals,

a and the video and sound signals.

The reference numerals. l1 and I8 designate sweeps and which are,respectively, at the desired field and line frequencies. Thelowfrequency sweep, by means of the amplifier l9, modulates thesub-carrier oscillator 20 in its amplifier stage 2|. The high-frequencysweep. by means of the amplifier 22, modulates the subcarrier oscillator23 in its amplifier stage 24.

The audio or sound signals from the micro phone 25 are passed through anamplifier 26.

The two modulated sub-carriers are combined with the audio signal in themixer 14 and the combination is'fed through the modulator 15 to modulatethe output of the oscillator 16 at the amplifier 11. The compositesignal upon the subcarrier from oscillator 16 is mixed with the videosignal in the mixer 18, after which, through;

modulator I9, the-single, ultra-high frequency carrier produced by theoscillator 19 is modulated at the amplifier 80 and radiated from theantenna 3|.

Although the two sweep signals are transmitted in the form of sinewaves,in Fig. 1 they are not used as such for direct application to the tworespective sets of electrostatic deflecting plates, but are firstchanged or modified to waves multiplying method for. the purpose of maintaining constant, particularly where interlaced scanning is used, therelation of line frequency to field frequency. A system or circuit forsuch purpose is shown in Fig. 6, in which a low-frequency voltage waveof sine form, such as the 60-cycle power main frequency, is fed throughsuccessive full-wave, rectifiers 31, 38, etc., followed by filters, asshown, to allow passage of the double-frequency harmonics. In this waythere is produced a final and much higher frequency which can beutilized for the high-frequency sweep coordinated with the originallowfrequency sweep for the two respective deflections for scanning. InFig. 6 there is shown only two stages of the frequency-multiplicationscheme. A'transformer primary 39 is excited by 60 cycles, and the tappedsecondary 40 supplies the fullwave rectifier 31 which delivers 120cycles to the tuned filter comprising the condenser 4| and thenexttransformer primary 42. The 120-cycle signal is supplied by the tappedsecondary 43 to the full-wave rectifier 38 and thence at the doublefrequency of 240 cycles to the condenser 44. and the next succeedingtransformer primary An alternative and simplified system or circuit,

for the same purpose as that shownin Fig. 6, is shown in Fig. '7. InFig. '7, the reference numerals 41, 48 and 49 designate transformerwind-' ings, connected as shown with respect to fullwave rectifiers 50and 5| and condensers 52 and 53.

In Figs. 6 and 7, conventional amplifier stages may be employed whenneeded. Also, if it is degenerators of voltage waves of sine form forthe sired to produce a phase relation of the final frequency,phase-shifting networks may be inserted in one or more stages of thefrequencymultiplication system. In cases where it is desired, as ininterlaced scanning, that the final,

high frequency be an odd multiple of the original low frequency, ratherthan an even multiple of the latter, it is proposed to use an excessnumber of doubler stages and then to employ one or more conventionalmultivibrator frequency-reduction stages to obtain the desiredodd-scanning frequency for the line sweep. i i At the receiver, as shownin Fig. 2, a superheterodyne circuit is employed, preceded by theradio-frequency amplifier stage 55 fed from the,

antenna 54. The detector 51 combines the received carrier with theoutput of the local oscillator 56. A wide-band, intermediate-frequencyamplifier 8| provides sufficient gain, and detector 82' then "deliverssignals to the two channels shown. The filter 83 passes only the videosignal. The intermediate-frequency stage 84 selects exclusively the subcarrier of 3M0, then detects its modulation at 63, and then delivers thetwo sweeps and, the audio signal to their respective channels throughthe filters 64, and 66. and

the detectors 6'! and 70;

The low-frequency sweep signal, still in the form of modulation upon itscarrier, is detected at 61 to produce in the output line a voltage wave.of sine form which is changed, by a wav l-form modifying network 69, toa saw-tooth voltage wave which is applied across the correspondingdeflecting plates. Likewise, the high-frequency sweep signal, still inthe form ofmodulation upon its carrier, is detected at '10 to produce inthe output line a voltage wave of sine form whichis changed by awave-form modifying network 12, to a saw-tooth voltage wave which isapplied across the corresponding deflecting plates.

The audio signal, in its original form from th filter B6, is fed to aloudspeaker 13. v

The video signal is applied to ascanning device 62. The device 62 isrepresented as being in the form of a cathode-ray tube of a commonconstruction, and comprising a fluorescent screen, an

, electron gun for developing a ray of electronsdirected at the screen,and two sets of electrostatic the intensity of the electron rayis madeto vary with the picture or video signals.

In Fig. 2, the unit 85 represents an automatic signal-level controlcircuit which, in the well known manner, utilizesa rectified portion ofthe received signal to adjust the bias on previous stages to aid inmaintaining substantially constantsignal output. In the present case,signal for the ,unit 85 is taken from the high-frequency sweep signalwill be steady and independent of background variations of the videosignal. As"

shown, the output control signal from the unit 85 is applied to controlbias in the first detector stagael51 and in theintermediate-frequencychannel Instead of transmitting sinusoidal sweeps as in Fig. 1, thegenerators I1 and I8 may be made to develop saw-tooth sweep wave forms,as shown in Fig. 3. Such a sweep wave form is characterized by having arelatively wide frequency band necessaryv for faithful transmission. Itsfundamental frequency and also its harmonics up to about the tenthshould be provided for. This type of scanp a very marked advantage ofthe present improved ning provides systematic and uniform coverage ofthe screen, and though high in harmonic contentcan still be used withthis system by proper design of the intermediate-frequency filters.

Another wave shape, illustrated in F12. 4, may be transmitted. in whichcase the generators l1 and I! are designed accordingly. It ischaracterized'by equal slopes of the forward and return traces, thuscontaining a much lower harmonic in the selective circuits at thetransmitter and receiver. I

It will be understood thatthe actual frequencies indicated in Figs. 1and 2 are by way of example only, and that these might vary widely tomeet particular requirements. In case the other shapes of scanningsignals are desired, it will be necessary to choose other frequencybands than here shown, but the general principles will be the same andare believed to i disclosed for those skilled viding a narrow'frequencyband and consequent simplified amplification and transmission of thesweeps.

Still. another feature of my improved system resides in the reducedvideo-frequency band possible with the multiple interlace or highinterlace ratio, yet giving high definition pictures. With this reducedvideo-band width and its relatively narrow associated band containingthe audio and the sweeps, it is practical to-utilize other and lowercarrier frequencies than those suggested in Figs. 1 and 2, and thus toemploy carriers which are not limited to an optical horizon forsatisfactory coverage.

i The frequency width of the video. signals illustrated in Figs. 1 and 2has been shown as those characteristic of a picture of about GOO-linedeflnition and the carriers chosen are merely suggestive. One can see.that even with this provision for a video channel of higher definitionthan provided in a unit with the 441-1ine standards with 2 to 1interlace,-the ultra-high frequency band still is not increased overthat required for the iii-line 2 to l interlace pictures. Now if only441 lines are. desired, using the system herein disclosed of multipleinterlace, and by very stringent selectivety in closely spaced channels,it is possible to reduce the channel band width to approximately 1megacycle each side of theultrahigh frequency carrier, thus makingpractical mthod-andsystem.

Another advantage of my improved system is that a receiver of the typeillustrated would be. versatile in its ability to accepttransmissionsfrom diii'erent stations utilizing diflerent degrees ofdetail up to a certain limit. Given a specified band pass in eachchannel. then pictures of any detail up to a certain limit could beaccepted by simply tuning to the appropriate R. 1''. carrier of thestation in question, without necessity of local achustment to duplicate.their particular sweep system. It will facilitate public heldinstallation of television systems without the fear' of equipmentbecoming immediately obsolete when definitlon changes are desired.

Another advantage of my improved system is the possibility of the use ofautomatic volume control, or automatic signal-level control byapplicatlon from one or the other fixed signals in the sweep circuits.Automatic control based on this signal will be steady and independent ofbackground variations of the video signal;

It has been foundthat excellent pictures may be obtained when integralratios between the scanning frequencies are purposely avoided. Thetelevision system herein disclosed allows practically any type ofinterlacing to be employed. For example, assume that there is employed avertical sweep of sixty fields per second, which is well beyond theflicker limit. Now a horizontal frequency of 3000 cylces per secondwould give fifty lines with exact progressive scanning. Now an increaseto 3030 cycles will provide 101 lines in the complete picture with a twoto one interlace ratio. The picture repetition rate is reduced to 30 persecond. but there is still no appreciable loss in picture continuity.Now

use some horizontal sweep such as 3002 cycles per second and thescanning will return to a given configuration only after half a second.This produces an effect of linesdrifting by when the pattern is greatlymagnified, but on the conventional viewing screen, the use of thisscheme employing other than integral ratios between sweep frequencies,makes the line structure practically indiscernable. Use of this peculiarratio of sweeps is practical with the'herein described televisionsystem, as it is necessary to regulate the sweeps only at thetransmitter.

A feature of my improved system resides in the utilization of actualscanning wave shape transmission suitable for electrostatic cathoderay'deflection, though with proper'ampliflers. the use of electromagneticdeflection is also pos-' sible. It is obvious that utilization ofelectrostatic deflection at the receiver would allow the same to followthe changes in scanning frequency or wave-form, whenthese might bevaried at the transmitter. It would be more diillcult to design anelectromagnetic system having this same flexibility.

Another feature of my improved system is the possibility of furthersimplification of the receiver equipment if operated on a common powermain with the transmitter, for then the power mainsfrequency may beemployed for the low sweep, reducing the complexity of the receiver inthat locality. However, the transmitter carrier may still ,contain thislow sweep component even when exciting such a receiver, for nodisturbance will be experienced if units 84 and M in Fig. 2 are omittedand replaced by suitable attachments to the power mains. In the light ofthis modifica tion, it would be most practical to secure the ment is alimit of the automatic signal-level\ control voltage from the high sweepchannel which will be present in all receivers. g V

Still another advantage of my improved system is that its receivers willbe versatile enough ning action thereat, the steps in the -method ofoperation which consist in generating video signals modulating asub-carrier with the highfrequency sweep wave, modulating a secondsubcarrier with the modulated first-named subcarrier, mixing the videosignal and the modulated second sub-carrier, modulating a mainultra-high frequency carrier with the resulting composite signal, andfeeding said modulated main carrier to radio transmission means.

2. In the art of television communication wherein it is required thatelectrical sweep waves of lowfrequency and highfrequency respectively besupplied to the receiver for governing the scanning action thereat, thesteps in the method of operation which consist in generating 'videosignals, modulating a first sub-carrier with the low-frequency sweepwave, modulating a segond sub-carrier with the high-frequency sweepwave, mixing the modulated first and second subcarriers with audiosignals, modulating a third sub-carrier 'with the resulting compositesignal, mixing the modulated third carrier with the video signal,modulating a main ultra-high frequency carrier with the final compositesignal, and feedingsaid modulated main carrier to radio transmissionmeans.

THOMAS T. GOLDSMITH, JR.

